Wilmington
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wilmington clear sky chart from 2005-11-06 to 2026-09-29.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	15% 6% 2 6% 4 4 5% 4 6% 8% 41%	149259
	Night	16% 7% 2 6% 4 4 4 3 5% 7% 43%	142108
Transparency	Day	27% 34% 8% 16% 12% 2	152804
	Night	28% 34% 8% 16% 12% 3	146649
Seeing	Day	17% 10% 26% 26% 15% 5%	17470
	Night	17% 8% 30% 32% 12% 1	26729

By Month

Percentage Cloud Cover NE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	13% 5% 2 6% 4 5% 4 4 5% 5% 46%	4661
	11th to 20th	Day	15% 7% 2 6% 4 4 3 3 4 5% 47%	4889
	21st to end	Day	16% 6% 2 5% 3 4 5% 4 6% 7% 43%	5780
February	1st to 10th	Day	14% 8% 2 6% 3 5% 5% 4 7% 7% 40%	1890
	11th to 20th	Day	17% 7% 3 6% 4 3 5% 4 5% 6% 40%	1990
	21st to end	Day	17% 10% 3 6% 3 4 3 2 5% 6% 40%	1730
March	1st to 10th	Day	20% 5% 2 4 3 3 4 3 4 6% 46%	4641
	11th to 20th	Day	13% 6% 2 5% 4 4 4 3 5% 7% 47%	5090
	21st to end	Day	18% 6% 2 5% 3 4 4 3 5% 6% 43%	5885
April	1st to 10th	Day	16% 6% 2 6% 5% 4 4 4 5% 7% 42%	2520
	11th to 20th	Day	14% 6% 1 5% 4 5% 4 4 6% 7% 43%	2494
	21st to end	Day	16% 6% 2 6% 4 4 4 4 6% 7% 40%	2520
May	1st to 10th	Day	23% 7% 2 5% 3 4 4 3 5% 8% 35%	7470
	11th to 20th	Day	20% 6% 2 5% 4 4 4 4 5% 7% 38%	8221
	21st to end	Day	24% 6% 2 6% 4 4 4 3 5% 7% 36%	9060
June	1st to 10th	Day	11% 6% 2 6% 4 5% 5% 4 6% 9% 41%	2940
	11th to 20th	Day	12% 6% 2 7% 4 4 5% 4 7% 9% 39%	2940
	21st to end	Day	10% 5% 2 6% 4 4 5% 4 6% 10% 42%	2940
July	1st to 10th	Day	10% 6% 2 7% 5% 5% 5% 4 7% 10% 39%	8280
	11th to 20th	Day	9% 6% 3 7% 5% 5% 5% 5% 8% 12% 35%	8280
	21st to end	Day	10% 5% 2 6% 5% 5% 5% 4 8% 11% 39%	8704
August	1st to 10th	Day	14% 6% 3 7% 5% 5% 6% 5% 8% 10% 31%	6014
	11th to 20th	Day	12% 5% 2 6% 4 4 5% 4 7% 11% 40%	5513
	21st to end	Day	9% 5% 2 6% 4 4 5% 5% 7% 9% 43%	6080
September	1st to 10th	Day	14% 6% 2 5% 4 4 4 4 6% 7% 45%	2520
	11th to 20th	Day	12% 5% 1 5% 3 4 4 3 5% 8% 49%	2500
	21st to end	Day	20% 8% 3 7% 4 4 4 4 5% 5% 36%	2268
October	1st to 10th	Day	16% 5% 2 5% 4 4 4 4 5% 6% 45%	2000
	11th to 20th	Day	16% 4 2 5% 4 3 4 4 5% 7% 49%	2000
	21st to end	Day	17% 5% 2 5% 3 4 3 3 4 6% 48%	2156
November	1st to 10th	Day	12% 6% 2 5% 3 2 3 4 4 7% 53%	1851
	11th to 20th	Day	15% 5% 1 5% 3 3 4 3 6% 7% 47%	1890
	21st to end	Day	15% 6% 2 5% 4 3 4 3 5% 6% 47%	1748
December	1st to 10th	Day	13% 7% 2 5% 4 4 4 4 5% 6% 46%	2680
	11th to 20th	Day	20% 9% 2 4 3 3 3 3 4 6% 43%	3066
	21st to end	Day	16% 6% 2 6% 4 4 4 5% 6% 8% 40%	4048
January	1st to 10th	Night	13% 7% 2 6% 4 4 4 3 5% 6% 45%	8234
	11th to 20th	Night	15% 8% 3 5% 3 3 3 2 4 5% 50%	7979
	21st to end	Night	16% 7% 2 5% 3 4 3 3 5% 6% 46%	8401
February	1st to 10th	Night	16% 9% 3 6% 4 4 4 3 5% 6% 41%	2730
	11th to 20th	Night	20% 6% 3 5% 4 4 3 3 5% 6% 42%	2515
	21st to end	Night	17% 7% 2 5% 4 4 3 3 6% 6% 41%	2076
March	1st to 10th	Night	18% 7% 2 5% 3 3 3 2 4 6% 46%	5402
	11th to 20th	Night	11% 8% 2 5% 4 4 3 3 4 5% 52%	5089
	21st to end	Night	15% 7% 2 6% 4 4 4 3 5% 5% 44%	5289
April	1st to 10th	Night	17% 7% 3 6% 4 3 4 3 5% 7% 41%	2100
	11th to 20th	Night	15% 6% 2 6% 4 4 4 3 5% 7% 43%	2075
	21st to end	Night	18% 5% 2 5% 4 4 4 3 5% 7% 44%	2100
May	1st to 10th	Night	20% 7% 3 7% 5% 4 4 4 5% 8% 33%	5457
	11th to 20th	Night	21% 7% 2 6% 4 4 4 4 6% 9% 34%	4639
	21st to end	Night	26% 7% 3 6% 3 3 3 3 4 6% 34%	5114
June	1st to 10th	Night	14% 6% 2 5% 5% 4 3 4 6% 8% 44%	1680
	11th to 20th	Night	11% 6% 3 7% 6% 5% 4 4 6% 10% 38%	1680
	21st to end	Night	11% 5% 2 5% 4 4 5% 5% 7% 10% 42%	1680
July	1st to 10th	Night	11% 6% 3 7% 5% 6% 6% 4 7% 10% 36%	4680
	11th to 20th	Night	11% 7% 3 7% 5% 5% 5% 5% 8% 12% 32%	4680
	21st to end	Night	12% 6% 2 6% 4 5% 4 5% 7% 8% 40%	5356
August	1st to 10th	Night	17% 6% 2 9% 5% 5% 5% 5% 6% 10% 30%	4135
	11th to 20th	Night	14% 6% 2 7% 5% 4 4 4 6% 8% 40%	4485
	21st to end	Night	12% 6% 2 6% 4 4 5% 4 5% 6% 47%	5045
September	1st to 10th	Night	13% 7% 2 6% 4 4 3 3 5% 7% 46%	2100
	11th to 20th	Night	13% 6% 2 4 3 2 3 2 5% 7% 52%	2119
	21st to end	Night	21% 7% 2 6% 3 4 4 3 5% 8% 36%	2304
October	1st to 10th	Night	19% 6% 3 6% 4 3 4 3 4 5% 44%	2400
	11th to 20th	Night	17% 4 2 5% 3 3 3 2 5% 6% 51%	2400
	21st to end	Night	16% 5% 1 6% 2 3 3 3 4 6% 50%	2682
November	1st to 10th	Night	11% 5% 2 5% 4 3 3 3 5% 6% 53%	2667
	11th to 20th	Night	16% 7% 2 5% 3 3 4 3 4 5% 48%	2730
	21st to end	Night	13% 6% 2 4 4 4 5% 4 6% 6% 46%	2867
December	1st to 10th	Night	13% 7% 2 6% 4 3 4 3 4 7% 48%	4720
	11th to 20th	Night	22% 6% 2 4 3 3 3 3 5% 7% 41%	5348
	21st to end	Night	18% 7% 2 5% 4 4 4 4 6% 6% 40%	7150

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	30% 22% 7% 21% 17% 2	4662
	11th to 20th	Day	33% 21% 4 19% 17% 6%	4920
	21st to end	Day	31% 23% 12% 22% 11% 1	5780
February	1st to 10th	Day	18% 60% 7% 8% 5% 1	1890
	11th to 20th	Day	20% 58% 3 9% 8% 2	1999
	21st to end	Day	19% 59% 4 11% 5% 2	1730
March	1st to 10th	Day	30% 29% 5% 16% 14% 7%	4644
	11th to 20th	Day	26% 29% 6% 22% 13% 4	5090
	21st to end	Day	29% 28% 8% 12% 17% 5%	5885
April	1st to 10th	Day	20% 59% 5% 8% 7% 2	2520
	11th to 20th	Day	16% 60% 6% 10% 6% 1	2494
	21st to end	Day	18% 60% 4 9% 8% 1	2520
May	1st to 10th	Day	38% 24% 11% 15% 11% 1	7479
	11th to 20th	Day	35% 24% 9% 21% 11% 1	8225
	21st to end	Day	39% 24% 7% 16% 12% 1	9061
June	1st to 10th	Day	16% 60% 3 10% 8% 1	2940
	11th to 20th	Day	16% 61% 4 11% 8% 1	2940
	21st to end	Day	15% 59% 5% 11% 9% 1	2940
July	1st to 10th	Day	31% 27% 13% 15% 13% 1	8210
	11th to 20th	Day	33% 26% 13% 20% 8%	8205
	21st to end	Day	29% 24% 8% 20% 18% 1	8511
August	1st to 10th	Day	35% 31% 15% 15% 4	6001
	11th to 20th	Day	26% 30% 13% 24% 7%	5549
	21st to end	Day	23% 29% 11% 22% 14% 1	6080
September	1st to 10th	Day	16% 56% 7% 11% 9% 1	2520
	11th to 20th	Day	16% 56% 5% 13% 8% 3	2500
	21st to end	Day	27% 55% 4 9% 5%	2268
October	1st to 10th	Day	20% 37% 5% 11% 22% 5%	3260
	11th to 20th	Day	12% 37% 8% 15% 22% 7%	3240
	21st to end	Day	9% 35% 8% 21% 23% 4	3458
November	1st to 10th	Day	16% 53% 7% 11% 8% 3	1851
	11th to 20th	Day	15% 55% 4 11% 14% 2	1890
	21st to end	Day	17% 54% 5% 16% 6% 1	1748
December	1st to 10th	Day	26% 35% 11% 16% 8% 3	2680
	11th to 20th	Day	31% 31% 7% 22% 7% 2	3066
	21st to end	Day	30% 28% 10% 17% 14% 2	4048
January	1st to 10th	Night	32% 21% 9% 19% 14% 4	8234
	11th to 20th	Night	30% 21% 6% 18% 17% 8%	8022
	21st to end	Night	32% 23% 6% 21% 16% 3	8401
February	1st to 10th	Night	18% 59% 6% 10% 4 2	2730
	11th to 20th	Night	19% 58% 3 8% 10% 2	2517
	21st to end	Night	17% 59% 5% 9% 6% 3	2076
March	1st to 10th	Night	32% 28% 6% 18% 8% 9%	5412
	11th to 20th	Night	23% 29% 11% 21% 12% 5%	5090
	21st to end	Night	31% 30% 6% 11% 20% 3	5289
April	1st to 10th	Night	20% 60% 3 9% 8% 1	2100
	11th to 20th	Night	16% 60% 6% 9% 8% 1	2075
	21st to end	Night	17% 59% 4 8% 9% 1	2100
May	1st to 10th	Night	39% 25% 9% 16% 9% 1	5464
	11th to 20th	Night	38% 24% 10% 21% 7%	4640
	21st to end	Night	43% 23% 7% 16% 10% 1	5115
June	1st to 10th	Night	16% 60% 3 10% 11%	1680
	11th to 20th	Night	18% 60% 5% 11% 7%	1680
	21st to end	Night	16% 59% 7% 11% 7% 2	1680
July	1st to 10th	Night	35% 25% 12% 17% 10% 1	4640
	11th to 20th	Night	35% 25% 15% 18% 7%	4632
	21st to end	Night	32% 25% 10% 18% 15%	5234
August	1st to 10th	Night	39% 32% 12% 12% 5%	4124
	11th to 20th	Night	29% 29% 12% 22% 8%	4515
	21st to end	Night	25% 29% 8% 24% 14%	5045
September	1st to 10th	Night	18% 55% 7% 11% 8% 1	2100
	11th to 20th	Night	17% 54% 4 12% 10% 2	2119
	21st to end	Night	26% 56% 4 8% 6%	2304
October	1st to 10th	Night	26% 38% 6% 12% 15% 3	3920
	11th to 20th	Night	12% 36% 6% 18% 24% 4	3899
	21st to end	Night	11% 36% 8% 22% 18% 5%	4330
November	1st to 10th	Night	16% 54% 6% 12% 8% 4	2667
	11th to 20th	Night	17% 54% 3 10% 13% 3	2730
	21st to end	Night	15% 55% 5% 15% 9% 1	2867
December	1st to 10th	Night	24% 35% 9% 22% 9% 2	4720
	11th to 20th	Night	31% 31% 7% 15% 11% 4	5348
	21st to end	Night	34% 28% 8% 14% 15% 2	7150

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	18% 21% 34% 20% 6% 1	220
	11th to 20th	Day	19% 32% 30% 16% 3	264
	21st to end	Day	19% 17% 39% 18% 5% 1	363
February	1st to 10th	Day	20% 21% 33% 20% 6%	330
	11th to 20th	Day	24% 18% 39% 16% 2	478
	21st to end	Day	20% 18% 36% 20% 5%	446
March	1st to 10th	Day	19% 20% 34% 21% 6% 1	540
	11th to 20th	Day	20% 19% 33% 22% 6% 1	540
	21st to end	Day	22% 15% 33% 23% 7% 1	594
April	1st to 10th	Day	22% 16% 35% 18% 8% 1	540
	11th to 20th	Day	17% 15% 32% 23% 11% 2	532
	21st to end	Day	20% 13% 28% 27% 10% 1	540
May	1st to 10th	Day	28% 13% 27% 20% 10% 2	543
	11th to 20th	Day	21% 9% 26% 28% 14% 2	567
	21st to end	Day	20% 7% 21% 24% 20% 8%	617
June	1st to 10th	Day	11% 8% 23% 31% 20% 7%	570
	11th to 20th	Day	15% 5% 27% 30% 17% 5%	570
	21st to end	Day	11% 6% 23% 32% 20% 9%	570
July	1st to 10th	Day	12% 4 15% 29% 28% 13%	565
	11th to 20th	Day	7% 1 13% 35% 30% 14%	564
	21st to end	Day	9% 4 17% 34% 28% 9%	620
August	1st to 10th	Day	11% 5% 16% 31% 25% 12%	566
	11th to 20th	Day	12% 3 14% 32% 28% 11%	559
	21st to end	Day	9% 3 21% 31% 23% 13%	627
September	1st to 10th	Day	15% 4 23% 25% 22% 11%	570
	11th to 20th	Day	14% 3 20% 29% 22% 13%	570
	21st to end	Day	27% 6% 22% 26% 15% 6%	562
October	1st to 10th	Day	21% 5% 18% 28% 17% 11%	530
	11th to 20th	Day	14% 12% 26% 25% 19% 4	530
	21st to end	Day	18% 7% 32% 26% 13% 4	558
November	1st to 10th	Day	15% 9% 32% 27% 15% 3	425
	11th to 20th	Day	16% 14% 34% 25% 11%	430
	21st to end	Day	15% 14% 35% 26% 8% 1	288
December	1st to 10th	Day	21% 16% 35% 20% 7%	220
	11th to 20th	Day	25% 15% 37% 16% 7%	220
	21st to end	Day	22% 18% 29% 19% 10% 2	242
January	1st to 10th	Night	18% 11% 43% 23% 4	840
	11th to 20th	Night	21% 13% 37% 25% 4	840
	21st to end	Night	18% 11% 42% 27% 2	924
February	1st to 10th	Night	19% 10% 40% 28% 2	840
	11th to 20th	Night	24% 13% 42% 20% 1	823
	21st to end	Night	20% 13% 42% 22% 3	692
March	1st to 10th	Night	18% 14% 37% 26% 5%	840
	11th to 20th	Night	18% 12% 40% 23% 6%	840
	21st to end	Night	19% 9% 42% 26% 5%	924
April	1st to 10th	Night	21% 14% 37% 22% 6%	840
	11th to 20th	Night	16% 10% 34% 34% 6%	831
	21st to end	Night	19% 8% 32% 34% 7%	840
May	1st to 10th	Night	19% 8% 34% 31% 8%	711
	11th to 20th	Night	17% 5% 33% 37% 8%	414
	21st to end	Night	19% 3 20% 37% 20% 2	455
June	1st to 10th	Night	15% 3 23% 40% 18%	420
	11th to 20th	Night	12% 5% 23% 45% 16%	420
	21st to end	Night	10% 2 20% 49% 19%	420
July	1st to 10th	Night	12% 1 17% 42% 26% 2	410
	11th to 20th	Night	6% 5% 12% 48% 28% 2	408
	21st to end	Night	9% 3 15% 44% 27% 2	553
August	1st to 10th	Night	12% 3 10% 44% 29% 2	627
	11th to 20th	Night	14% 3 12% 39% 29% 3	796
	21st to end	Night	13% 3 15% 38% 27% 3	924
September	1st to 10th	Night	15% 3 19% 37% 24% 2	840
	11th to 20th	Night	14% 3 13% 39% 27% 4	840
	21st to end	Night	24% 4 19% 32% 20% 1	833
October	1st to 10th	Night	21% 5% 22% 29% 19% 4	800
	11th to 20th	Night	18% 6% 26% 36% 13% 1	800
	21st to end	Night	19% 7% 32% 31% 11% 1	880
November	1st to 10th	Night	13% 7% 33% 35% 12% 1	820
	11th to 20th	Night	20% 9% 33% 30% 8% 1	840
	21st to end	Night	15% 11% 37% 28% 8%	840
December	1st to 10th	Night	21% 12% 34% 26% 7% 1	840
	11th to 20th	Night	19% 9% 37% 30% 6%	840
	21st to end	Night	21% 9% 36% 31% 3	924

Page generated at 2026-09-26 04:18:44. Version ac07

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